The present invention relates to a hollow package manufacturing method and apparatus for applying to a hollow package cap an adhesive used for adhering the hollow package cap to a case.
Ultra-high-frequency devices include transistors, ICs, optical elements, surface acoustic wave elements, resonators, and the like. Conventionally, since these devices are used in commercial communication apparatuses and satellites, they must have a high reliability and a long service life even though they may become somewhat expensive. Recently, many ultra-high-frequency devices are also used in home-use apparatuses such as receivers for broadcast satellite communication, portable telephones, and the like. Although devices used for home-use apparatuses do not need such a high reliability and a long service life as those of the commercial communication apparatuses, they must be manufactured at a low cost as much as possible. Among attempts for manufacturing lower-cost devices, an ultra-high-frequency chip conventionally sealed in a ceramic package is incorporated in a hollow package made of a synthetic resins thereby reducing the cost.
A resin-molded package of this type is formed by adhering a cap to a case mounting a semiconductor chip and the like therein. As an adhesive used for adhering the cap to the case, a sheet-like adhesive or a liquid adhesive is used. A conventional method of forming a hollow package by using a liquid adhesive will be described with reference to FIGS. 10A to 10E.
Referring to FIGS. 10A and 10B, reference numeral 1 denotes an adhesive coating unit. The adhesive coating unit 1 spreads a liquid adhesive 2 having a viscosity over the upper surface of a mask 3 with a squeegee 4. A plurality of mask openings 3a having the same shape as that of adhesion surfaces are formed in the mask 3 and are positioned above hollow package caps 5 (to be described later).
The hollow package caps 5 are made of a synthetic resin into cylinders respectively having bottoms and recessed portions 5a, and are held by a tray 6 such that their end faces 5b where the recessed portions 5a are open face upward. The tray 6 holds the caps 5 to face upward at positions corresponding to the mask openings 3a of the mask 3. Each mask opening 3a is formed to have a hole diameter substantially equal to the outer diameter of the cap 5.
Referring to FIG. 10C, reference numeral 7 denotes a heating furnace. Referring to FIG. 10D, reference numeral 8 denotes a vacuum suction nozzle for conveying the cap 5 coated with the adhesive 2 downward. Hollow package cases 9 are formed by molding the synthetic resin on a lead frame 9a. A wire-bonded ultra-high-frequency semiconductor chip 9b is mounted in the hollow package case 9. Referring to FIGS. 10D and 10E, reference numeral 10 denotes a heater plate for heating the placed hollow package case 9. As the synthetic resin that forms the caps 5 and the cases 9, an epoxy resin is employed. As the adhesive 2, one containing an epoxy resin as the major component is used.
In the conventional arrangement described above, to adhere the caps 5 to the hollow package cases 9, first, the adhesive 2 is applied to the end faces 5b of the caps 5 by using the adhesive coating unit 1, as shown in FIGS. 10A to 10C. More specifically, the caps 5 are held by the tray 6 and their open end faces 5b are positioned below the mask openings 3a of the mask 3, and the adhesive 2 is spread over the mask 3 with the squeegee 4. Therefore, the adhesive 2 fills the mask openings 3a of the mask 3 to coat the end faces 5b of the caps 5.
Thereafter, the tray 6 is separated downward from the adhesive coating unit 1. The adhesive 2 coating the end faces 5b of the caps 5 is separated from the adhesive 2 on the surface of the mask 3 to remain in the caps 5. The thickness of the adhesive 2 applied to the open end faces 5b corresponds to the thickness of the mask 3. Accordingly, when the thickness of the mask 3 is changed, the adhesive 2 can be easily applied to a desired thickness
As shown in FIG. 10C, the caps 5 are supplied together with the tray 6 into the heating furnace 7 and are heated in order to semi-harden the adhesive 2. This aims at preventing the caps 5 from adhering to each other or from adhering to a transfer vessel (not shown) when the caps 5 are transferred to a following step.
After the caps 5 are extracted from the heating furnace 7, they are loaded in the transfer vessel (not shown) and are transferred to the cap adhering unit shown in FIG. 10D. Subsequently, the caps 5 are extracted from the transfer vessel with a handling unit (not shown) and are aligned to discriminate their vertical and horizontal directions. The bottom surface (a surface opposite to the open end face 5b applied with the adhesive 2) of each cap 5 is drawn with the vacuum suction nozzle 8.
Thereafter, the cap 5 facing downward is conveyed above the case 9 with the vacuum suction nozzle 8, as shown in FIG. 10D, and is urged against the upper surface of the case 9 which has been placed on the heater plate 10 and heated. The adhesive 2 is heated and melted by the heat of the case 9, and is hardened, so that the cap 5 is adhered to the case 9 through the adhesive 2.
When a sheet-like adhesive is used as the adhesive 2, it is cut into the same shape (annular shape) as that of the open end face 5b of the cap 5, and the cut adhesive sheet is adhered to the open end face 5b. Thereafter, the cap 5 is adhered to the case 9 through the adhesive sheet.
The most significant element in the adhesive coating step is how to apply the adhesive in a desired thickness accurately. For example, if the amount of adhesive 2 applied to the cap 5 is smaller than the defined amount, the cap 5 cannot be firmly adhered to the case 9, and moreover the airtightness at the adhesion portion is decreased. Inversely, if the amount of applied adhesive 2 is larger than the defined amount, an excessive adhesive 2 flows into and out of the package to degrade the outer appearance, or attaches to the chip and wires to degrade the electrical characteristics. From these reasons, conventionally, the thickness of the adhesive 2 is strictly managed to fall within a range of 20 .mu.m to 50 .mu.m by controlling the thickness of the mask or the thickness of the sheet-like adhesive film.
When, however, the method shown in FIGS. 10A to 10E is employed, the mask opening 3a and the open end face 5b of the cap 5 must be aligned at high precision. The conventional cap 5 has a comparatively large size and thus can be aligned easily. In contrast to this, since the package for an ultra-high-frequency device has a small diameter of 2 mm and its recessed portion-side end face 5b has a small width of 0.25 mm, alignment must be performed with an error of 0.02 mm or less. If misalignment occurs, the liquid adhesive 2 may leak to the outer circumferential portion of the cap 5 through a gap formed by misalignment, or some region of the open end face 5b may be left uncoated with the adhesive 2, leading to a poor outer appearance and a decrease in reliability. From these reasons, a long period of time is required for alignment, and a high-precision, expensive alignment unit is indispensable, increasing the manufacturing cost of the device accordingly.
In this manner, since the adhesive coating unit 1 using the mask 3 has a complicated arrangement, it must be inevitably separated from the cap adhering unit. Therefore, when transferring the caps 5 from the adhesive coating unit 1 to the cap adhering unit, a countermeasure must be taken so that the caps 5 will not adhere to each other or adhere to the transfer vessel. Conventionally, the adhesive 2 coated by the adhesive coating unit 1 is placed in the heating furnace once and is semi-hardened so that its adhesion properties are decreased, and thereafter the caps 5 are transferred.
For this purpose, a heating unit for semi-hardening the adhesive 2, the transfer vessel used for transfer between the steps, the handling unit for transferring the caps 5 to the cap adhering unit, and the like are required. Also, during handling, the caps 5 must be aligned again and their vertical direction and referential direction must be discriminated. Furthermore, when adhering the caps 5, the adhesive 2 must be preheated to restore it from the semi-hardened state to the molten state. In this manner, with the method using the mask 3, although the thickness of the adhesive 2 can be uniformed comparatively easily, expensive units and a large number of steps are required for alignment and handling.
When the sheet-like adhesive is used, although a heating furnace for semi-hardening the adhesive becomes unnecessary, high precision is required in alignment, in the same manner as for alignment of the mask 3. Since the sheet-like adhesive need be attached with parting paper or the like to facilitate its handling, the sheet-like adhesive itself becomes expensive. In the package for the ultra-high-frequency device, since the sheet has a small diameter of 2 mm and a small width of 0.25 mm, even if the sheet is cut circular with a die, when adhering the sheet to the cap 5, the sheet may be deformed to cause misalignment in the adhesion position. As a result, the adhesion strength is decreased, or the airtightness may be decreased.